When it's H1B, it's a pretty sure shot visa stamping process. But, it's better to be prepared than underprepared.

I would recommend few things (this might vary between people depending upon what stages of H1B they are in):

1. Your' initial I20 (the one you came to US with, again folks already in H1B before  and are needing visa because of job switch may not need to dig this deep).

2. Int'l student office must have given you a new I20 when they applied for your OPT

3. Your OPT card.

4. Transcript and conferred degree

5. H1B approval notice

6. Bank statement (this is not a requirement, but planning for a worst case scenario, and money in the bank is not a limiting factor when you are H1B, unless you have dependents)

7. A letter from employer clearly stating that you are working on H1B for them, job start date, your designation, and few lines describing your duties. Also how many hours you work/week, your allowed vacation/PTO/sick leave time, medical insurance coverage. The latter part is more for Nepalese labor department than US Counslar. I believe now they require you to get a labor permit before you can depart from Nepal.

8. A copy of H1B application obtained from your lawyer (again preparing for worst case scenario)

Few more suggestions.

Go to US Embassy website and fill and print out all the required form before hand. In Nepal it will be more confusion to work thru  electricity, internet, printers etc.

And, get a "Photo Concern" type photograph, I would recommend taking it in Nepal itself. Personnel in Nabil bank are used to seeing certain type of picture, any deviation from it and you might have to undergo unwanted hassle.

Good Luck!